1. Field of the Invention
This invention provides a process for producing allyl acetate, 1-propenyl acetate or mixtures thereof by dehydroformylating 4-acetoxybutyraldehyde, 2-acetoxybutyraldehyde, 3-acetoxy-2-methylpropionaldehyde or mixtures thereof. This invention also provides an improved process for hydroformylating these products to 4-acetoxybutyraldehyde and an improved process for making 1,4-butanediol from propylene, acetic acid and oxygen.
2. Description of the Prior Art.
In my copending application A, Ser. No. 365,228 filed May 30, 1973 now abandoned, and assigned to the same assignee as the present invention, I have disclosed and claimed a process for making butanediols by oxidatively coupling propylene and acetic acid to produce allyl acetate which is then hydroformylated to produce the mixture of three isomeric acetoxybutyraldehydes. Hydrogenation of the mixture produces a mixture of isomeric acetoxybutanols which can also contain some of the diesters and free diols. In my copending application B, Ser. No. 365,231, filed May 30, 1973 now abandoned, and assigned to the same assignee as the present invention, I have disclosed and claimed a process wherein the hydrogenation is accomplished during the hydroformylation reaction. De-esterification of the acetoxybutanol mixture produces the desired butanediols which can be separated by distillation.
In my copending application C, Ser. No. 371,714, now abandoned, filed concurrently herewith and assigned to the same assignee as the present invention, I have disclosed and claimed that hydroformylation of 1-propenyl acetate under hydroformylating conditions in the presence of a cobalt hydroformylation catalyst yields essentially the same isomeric mixture of acetoxybutyraldehydes as is obtained from allyl acetate.
Prior to my discovery, the prior art, see for example J. Am. Chem. Soc. 70, 383 (1948) and 71, 3054 (1949), reported that the hydroformylation of allyl acetate led to only one product, 4-acetoxybutyraldehyde, in essentially a 70-75% yield. Although my work confirms this yield, I have also found that the balance of the allyl acetate has been converted to two isomers of the 4-acetoxybutyraldehyde, specifically, 2-acetoxybutyraldehyde and 3-acetoxy-2-methylpropionaldehyde in approximately equimolar amounts.
Although, as shown in my copending applications A and B referred to above, these two isomers can be converted to their corresponding butanediols, specifically 1,2-butanediol and 2-methyl-1,3-propanediol, neither of these two products are as desirable as 1,4-butanediol, which forms polyesters with dicarboxylic acids, such as terephthalic acid, which are commercially much more desirable than the polyesters obtained from the other two isomers. It would be highly desirable, therefore, to be able to obtain higher yields of the 4-acetoxybutyraldehyde either by decreasing the production of the other two isomers or by converting the latter into the desired isomer.
Insofar as I am aware, the only attempt to recycle an undesirable by-product of a hydroformylation reaction is described in British patent 1,241,646, its corresponding counterparts in other foreign countries, and in articles written by the inventors and coworkers, see for example, Angew. Chem., Internat. Edit. 9, 169 (1970) and 11, 155 (1972), Ind. Eng. Chem. 62 [4] 33 (1970). These references describe that in the hydroformylation of propylene to n-butyraldehyde, isobutyraldehyde is obtained as a less desired product. This latter product is dehydroformylated to propylene, carbon monoxide and hydrogen which can then be recycled in the hydroformylation reaction to increase the yield of the n-butyraldehyde in the over-all reaction. Other related art in this area teaches the production of saturated aliphatic compounds arising from the hydrogen interaction with the dehydroformylation product to hydrogenate the olefinic double bond. This latter reaction is called decarbonylation because, in effect, only carbon monoxide is removed from the starting product.
One of the convenient means for converting a compound containing an alcoholic hydroxyl group to an olefin is to make the acetate ester of the compound which is then thermolyzed or pyrolyzed to produce the olefin and acetic acid. For convenience, this ester thermolysis reaction, as applied to acetate esters, will be called dehydroacetoxylation since a hydrogen is removed from one carbon atom and the acetoxy group from the adjacent carbon atom to form acetic acid and create an olefinic double bond in the initial compound. Since the isomeric acetoxybutyraldehydes, to which this invention is directed, are acetate esters as well as aldehydes, they could undergo (a) the dehydroacetoxylation reaction to produce unsaturated aldehydes, (b) both the dehydroacetoxylation reaction and the hydrogenation reaction to produce saturated aldehydes, (c) the dehydroformylation reaction to produce unsaturated esters, (d) the dehydroformylation and hydrogenation reaction to produce saturated esters or (e) any combination of (a) through (d). It was indeed surprising to find that the dehydroformylation reaction could be effected with the other reactions occurring to a minimal extent.